Vegetables are known for their ability to help you maintain a healthy weight, control blood pressure and blood sugar levels, and reduce risk of heart disease and stroke — benefits that are derived directly from the nutrients in the plant. However, the way you prepare vegetables makes a difference in the amount of nutrients available for the body to take up. The three main factors that control the nutrient content of vegetables in cooking are temperature, time and water amount. Lower temperatures, less time exposed to heat and as little added water as possible are the surest ways to unlock the maximum nutrients your vegetables have to offer. Here is the healthiest way to cook vegetables.

Cooked vs. raw: Both are beneficial

To optimize your nutrient intake, it’s best to eat a combination of both cooked and raw vegetables.

Cooking has a mixed effect on nutrients, destroying some vitamins, antioxidants, and minerals in some foods, but increasing them in others. For example, vitamins C and E — along with some enzymes — are extremely sensitive to heat, although different heating methods have varying effects. Steaming and baking lose the least amount of these nutrients, while boiling and frying lose the most. 

On the other hand, some vitamins and minerals, such as carotenoids (e.g., vitamin A and beta-carotene) are stored in the strong and fibrous cell walls of plants, and these walls are not easily broken by simple mastication. Under heated conditions, the cell walls burst, releasing the nutrients inside; thus, steaming, boiling and baking vegetables actually increases the amount of those nutrients. Similarly, the antioxidant lycopene is released under the same temperatures, so you’ll get more lycopene from heated tomatoes or tomato/spaghetti sauce (rich in lycopene) than you would from raw, fresh tomatoes.  

Fresh, frozen, or canned: Which form is healthiest?

The moment a vegetable is cut from the mother plant, it begins to lose vitamins and nutrients. A plant continues to live after it’s harvested, taking in oxygen and using the stores of vitamins and minerals in its cells, leaving fewer nutrients for us to ingest when we finally consume the produce.

Most canned and frozen vegetables are processed within a few hours after harvesting, so the nutrient (and flavor) losses are minimal. Depending on how long it’s been from when the head of broccoli was harvested at the farm to when you picked it up from your local grocery store shelf, the frozen or canned version may even be fresher and more nutrient-dense: 

• Freezing pauses the oxidation process in vegetables, which mitigates the nutrient loss caused from storage and transport times and temperatures. 
• Canning is similar (in that the process pauses oxidation), but because most produce is canned in a water solution, some nutrients are lost to the surrounding water. Further, many canned vegetables contain high levels of sodium or other preservatives that are unnecessary or even detrimental to your health: check the label before buying canned vegetables.
• Other types of preservation that require heating result in much more significant nutrient loss. 

Thus, the best vegetable to buy, if not fresh, is frozen. 

Additional factors that impact the nutrient density of your vegetables prior to cooking include the soil quality in which the vegetables grew, as well as how the plants were harvested, transported and stored.

• Soil gives a plant its nutrients. Poor soil, which is dry soil lacking biological activity, doesn’t provide a vegetable with the vitamins and minerals that we hope to ingest. There isn’t a universal identifier on the label that denotes the soil health of the farm where the vegetable came from, so unfortunately consumers are blind to this information. 
• Harvesting can occur either by hand or machine. Machine harvesting is usually used in large-scale production, so most of the vegetables you buy in a grocery store come to you that way. Harvesting, transporting and storing impacts nutrient density in two ways: when a fruit or vegetable gets bruised or torn, the plant goes into defense mode and loses nutrients more quickly in an attempt to heal itself. Delicate vegetables (such as  salad leaves, tomatoes, and asparagus) can get damaged easily, whereas root vegetables (think turnips, parsnips, carrots, and radishes) are more hardy. 

The healthiest way to cook vegetables

No matter what cooking method you choose, the best guidelines to begin with for the healthiest way to cook vegetables are to:

• Use the entire vegetable.
• Add in flavors you love through spices and seasonings.
• Keep sodium and added calories (i.e., butter and oils) to a minimum.

Then, if you’re planning to cook your vegetables, the surest ways to unlock the maximum nutrients in them are to use:

• Lower temperatures
• Less time exposed to heat
• As little added water as possible 

Of all of the ways to cook vegetables, frying and boiling lose the most nutrients because nutrients easily seep out into the oil or water. 

However, there isn’t one cooking method that’s a catch-all for releasing nutrients for vegetables. Here are the go-to methods that can be used on a rotating basis that can help maximize nutrient availability for cooking. 

Steaming

Steaming veggies preserves nutrients, color, shape, and texture without having to add any unnecessary fats through ingredients like oils or butter. Steaming increases the amount of carotenoids, as well as some antioxidants and phytochemicals, and maintains the quality of most micronutrients. Steaming is preferable to boiling because in the latter nutrients get lost in excess water. To steam, place food in a metal or bamboo steam basket over boiling water and cover. When the vegetables reach peak brightness, they’re ready. As soon as the vegetables begin to dull in color, they are overcooked. 

Microwave

Microwaving is similar to steaming and it’s easy and quick. The process of microwaving heats the water and fat molecules in a food and avoids browning, avoiding many carcinogenic compounds caused by high-heated cooking. To microwave, place vegetables in a microwave-safe dish, add a small amount of water and seasoning, and partially cover. Be sure to avoid adding too much water or overcooking to where the vegetables dulls in color. 

Sautéing

Cooking for too long and at high temperatures can result in oils oxidizing and forming cancer-causing heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). But sautéeing, while using high heat, is done quickly — so it’s a good option as long as you keep the cooking time short (just a few minutes) and use a healthier oil with a high smoke point (e.g., avocado oil, sesame oil, safflower oil) sparingly. To sauté, heat a pan under medium-to-high heat, then add the oil, vegetables and seasonings for a few minutes. The high heat sears the vegetables quickly, locking in important nutrients and maintaining the color and texture of the vegetables. 

Baking or roasting

Roasting vegetables exposes them to high heat for longer periods of time, which can decrease nutrients and increase potentially carcinogenic compounds. The benefit of roasting is that it brings out flavors in vegetables that other cooking methods do not. Especially for vegetables that take a longer time to cook, such as squash or other root vegetables, steam them and then lightly coat with a high-smoke-point oil and seasoning, and then bake. This method shortens the amount of time under high heat, retaining nutrients while still exposing flavors. 

Grilling 

In 2007, The World Cancer Research Fund released a report on Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, recommending that people avoid eating burned or charred foods frequently or in large quantities. Most epidemiological studies suggest a link between eating a lot of overcooked, fried, and grilled meats and certain types of cancer.

Cooking over high heat, such as grilling or broiling, can result in carcinogenic formation of heterocyclic aromatic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), compounds that research has shown to have cancer-causing effects. HCAs develop when certain amino acids and a muscle protein called creatine react in high temperatures, increasing as time in heated conditions continues. PAHs are produced when fats burn and then stay attached to the meat. PAHs are also found in cigarette smoke and air pollution. And while vegetables don’t contain creatine and therefore don’t create HCAs, the charing that grilling or broiling causes can still create carcinogens such as benzopyrene. 

But can grilling still be healthy for you? Yes, but in moderation and by avoiding excessive charring and browning by shortening the grill time and flame exposure. 

Key takeaways

What is the healthiest way to cook vegetables? Consumption of both raw and cooked vegetables are necessary parts of a healthy eating pattern. (To better understand why vegetables are so critical to human health, see the following reports: What is fiber?; How consuming more fiber can benefit diabetes management; and Beginner’s guide to starting a plant-based diet.) The healthiest way to cook vegetables is steaming because it uses a low heat for a short amount of time without adding water that can steal away valuable nutrients. However, there are a variety of other ways to cook vegetables that retain most nutrients and contribute to your health while offering flavorful, satisfying components of a meal. Beyond focusing on the cooking method, choosing the freshest and most nutrient-dense form of vegetables, whether that be fresh or frozen, also makes a difference to the end result. So, too, does the actual type of vegetable you choose: if you’re watching your blood glucose level, vegetables that score low on the Glycemic Index (GI) and Glycemic Load (GL) scale — such as broccoli, Brussels sprouts, asparagus, artichokes, mushrooms, and bok choy — will likely have less of a tendency to spike your blood glucose than higher-scoring vegetables such as potatoes or corn.

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